In draining fluid from a body cavity or wound to promote healing, such as after chest surgery, a catheter and a drain tube are usually connected to drain the fluid into a drainage collection system either by the force of gravity alone or with the assistance of suction. Usually, the system includes an underwater seal "bottle" or chamber in series with a source of suction. In closed cavity or wound drainage systems where there is no air leak or air flowing into the cavity, drainage fluid flows from the cavity as the walls of the cavity tend to approximate or come together. Once the walls substantially approximate, the system tends to become static with the pressure in the cavity becoming substantially equal to the underwater seal collection system pressure, even though drainage fluids may remain in the catheter and drain tube, and even some in the cavity. Also, blood clots may clog the catheter such that fluids no longer readily drain into the underwater seal collection system but tend to build up in the catheter and/or drain tube.
In order to restore proper drainage in a static system, it is sometimes necessary to vent the body cavity thereby providing the force necessary to remove drainage fluids. One method of venting the cavity has been to clamp off the catheter and disconnect it from the drain tube. After reconnection, air in the tube reduces the negative pressure in the cavity. This procedure requires time and effort on the part of the attendant or nurse and may allow bacteria to enter the cavity. In an attempt to provide some filtering, cloth or the like has been placed over the open end of the tube. Another method is to discontinue the suction and introduce filtered air through a hypodermic needle and filter, for example, by inserting a needle into the drain tube and allowing air to enter the system and reduce the pressure in the cavity. Disconnecting the drain tube and the use of a filtered needle, of course, are unhandy methods and only provide a given amount of air at a time. Also, these methods may have to be repeated several times during a drainage collection procedure.
It is also common practice to strip the drain tube in order to pull blood and clots in the wound space into the collection tubing. This stripping is done by hand squeezing the tube and moving the hand toward the underwater seal collection system. This can, however, result in excessive negative pressures being applied to the cavity. Such excessive negative pressures may damage delicate tissues, cause excessive drainage and make drainage less efficient as the higher negative pressures pull tissues into and clot catheter eyes. In order to reduce the negative pressures to the desired value in the chest wound after stripping, air has been introduced into the cavity by the undesirable methods mentioned above.
Multi-lumen catheters have been used in which one of the lumens is connected to the atmosphere through a filter to vent the body cavity. However, depending upon the flow rate of air into the cavity, such air flows through the catheter drainage tube and bubbles through the usual underwater seal of the chest drainage suction system and this can result in excessive evaporation of the seal. Such venting does not provide a controlled degree of venting or controlled negative pressures in the cavity, and does not allow adjustment of the amount of air bubbling through the underwater seal. Uncontrolled or an excessive amount of gas bubbling into the underwater seal increases the risk that the seal will fail and allow the reverse passage of gas back to the body cavity. Also, the usual stripping of the drainage tube in order to obtain momentary high negative pressures in the cavity so as to remove clots from the eyes of the catheter is not possible where relatively high air flow venting of the cavity is provided.